The invention is in the field of sonar. In the prior art, the high power acoustic output of a sonar transducer has been severely limited by cavitation in the water surrounding the transducer. Cavitation interferes with the transfer of energy from the transducer to the water. Sonar transducers affixed to ships and submarines are usually enclosed in a streamlined dome or bubble which contains water. The cavitation level of the water in the dome is critical, because this water is the medium through which the energy developed by the transducer is conveyed to the water outside the dome. Various expedients such as degassing the water by applying a surface vacuum, prepressurizing the dome to high hydrostatic pressures, processing to attain ultra-pure water, etc., have been tried. These expedients are in general expensive and require complex and cumbersome apparatus. Pressurization can rupture the dome or distort its streamlined shape. Applicant's invention solves this problem of the prior art by providing simple, convenient, inexpensive, and effective means for retarding cavitation in water.